The invention concerns a sample holder for the introduction of a sample substance for transmission measurements with optical radiation into a spectrometer, in particular, an infrared spectrometer said sample holder being at least partially made from a material which is transparent in an interesting wavelength region of the optical radiation and exhibiting an index of refraction in excess of 1.
Such a sample holder is, by way of example, known in the art from the article 459 of A. M. Haefner et al. in the Book of Abstracts of the Pittsburgh Conference from Mar. 6, 1989 through Mar. 10, 1989 in Atlanta, USA. The sample holder which is known in the art consists of an approximately plane parallel plate upon which a sample substance initially dissolved in a solvent, which, by way of example is taken from a chromatograph, is deposited in the form of a drop. One then allows the solvent to vaporize or to evaporate so that a layer of the sample substance remains, in powder form, on the sample holder which is examined in diffuse transmission. A disadvantage of the procedure which is known in the art is, when introducing the drop onto the flat sample holder, the solvent spreads out over the surface of the sample holder and after evaporation or vaporization of the solvent the sample substance is distributed over a relatively large surface area, whereby there is moreover a tendancy for the sample substance to accumulate largely on the borders of the deposited liquid where it is therefore present in substantially higher concentrations than in the middle of the deposited drop. In particular, if the plane parallel surfaces are not kept exactly horizontal when introducing the drop onto the sample holder then the fluid with the sample substance can spread over the surface of the sample holder and thereby distribute itself over a still larger surface area. Furthermore, a great amount of light is lost in the subsequent transmission measurement in that, after passing through the surface containing the sample substance, said light is emitted at large angles from the optical axis of the ray path.
Known in the art from the article 249 of K. H. Shafer et al. in the Book of Abstracts of the Pittsburgh Conference in Atlantic City, USA, from Mar. 10, 1986 through Mar. 14, 1986 is a procedure with which the sample substance is introduced onto an infrared transparent powder, by way of example KCI, diamond or glass located in a cup-shaped depression of an aluminium strip. A spectrum of the sample substance is subsequently taken in diffuse refraction. A disadvantage of this method is that the reflection measurement requires an extensive set-up and is less sensitive and also less reproducible than a transmission measurement.